Wide band antenna



06L 195'1 N. E. LINDEINBLADY 2,570,824

WIDE BAND ANTENNA Filed July 4; 1945 Y s Sheets-Sheet 1 PEQCZWT au/vsz //v FREQUENCY IN VENT 0.2;

T TOR/ 5 y 1 1951 N. E. LINDENBLAD 2,570,824

, WIDE BAND ANTENNA Y Filed Ju iy 4, 1945 v s Shegts-Sheet 2 4 f 1 0 a 1 v TTORNEY 9, 1951 N. E. LINDENBLAD WIDE BAND ANTENNA 3 Sheets-Sheet 5 Filed July 4, 1945 //v|//vTOR M45 5. L uv mvsmp A T OR/VEy f atenteci umrao STATES PATENToFFic-Ei 2576324 7 WIDE BAND ANTENNA I Nils E. Lindenblad, Rocky Point, N.- Y.; assignor to Radio Corporation of America, a corporation of Delaware Application July 4, 1945, Serial No. 603,211 25 Claims. (01. 250-33) The present invention relates to wide band antennas and, more particularly, to slot antennas adapted to be flush mounted in the skin of aircraft.

An object of thepresent invention'is the provision of a wide band slot antenna.

Another object of the present invention is the provision of an antenna which from aerodynamic considerations is ideally adapted to aircraft use. I

. A further object of the present invention is the provision of a slot antenna which does not require extensive cavities beneath the skin of the aircraft.

A further object of the present invention is the provision of a slot antenna having a bandwidth of several percent.

Still a further object of the present invention is the provision of a sheet antenna which does not require isolating slots around the periphery of the radiating area.

I Still a further object of the present invention is the provision of a wide band slot antenna which does not require the use of complicated compensating circuits to obtain the required band width.

Antennas of the slot type previously invented by me utilize two parallel slots in a conductive sheet, said slots being separated by a distance equal to a half of the operating wavelength. The concept involved in such antennas is that the half wave wide ribbon between the slots is resonant at the operating frequency. The high impedance slots isolate the ribbon from the surrounding surface so that only stray field currents flow in the surrounding surface, thus assuring a radiation pattern which is unusually free from deleterious'side lobes.

The present invention contemplates utilizinga single feed slot inthe radiating area asan energizing means for producing a radiating current pattern therein.

Since the aim with all slot antennas is to produce a surface current pattern which radiates in certain desired directions, many modifications can naturally be made without deviating from the basic principles of operation of the antenna. In one embodiment of the present invention the half Wave wide ribbon of the previous an,- tennas may be replaced by two 9Q degree triangles, having their bases connected to the central feed slot. The outer insulating cavities may then be bent around the other sideof the tri-. angles and some space conserved. A hybrid between, ribbon n s ne eislot anten a hu obtained. By means of the use of 'a conductive 2 I wedge in the coupling circuit as a connection be tween an edge of the slot antenna and the center conductor of a coaxial transmission line, it-was found that a bandwidth of about nine percent could be obtained. The use of a more obtuse feed triangle between the antenna and the transmission line-resulted in a bandwidth in excess of sixteen percent. Band width isherein based on less than 2:1 standing wave ratio on the feed line.

In .accordancewith another aspect of thepresent invention the size of the antenna maybe further reduced by removingthe outer high impedance boundary cavities. The removal of these boundary cavities does, of course, result in radiation patterns having side lobes of relatively greater magnitude since the currents in the ra: diating plane theoreticallyspread out indefinitely and thus should contribute to the formation of sideilob es. The spread is however s diso'rganized and attenuated as far' as forming standing waves from reflection at the remote free edges of the radiating'sheet is concerned that the bulk of the radiation may be considered to take place from the current in the immediate vicinity of the feed slot. Such'patterns are acceptable exceptin certain exacting radar applications The present invention will be more full under-'- stood by referenceto the following detailed de-' scription which is accompanied by a drawing in Figure 1 illustrates in plan' view an embodiment of the present invention while Figure 2 is a sectional view taken along the line 22' of Fi ure 1.

Figure 3 is a curve illustrating graphically a bandwidth obtained with the antenna of Figures 1and2."

Figure 4 illustrates in plan view amodified form of the present invention while Figure 5 is a sec-'- tional -view' of theantenna of Figure 4, taken along line55, and

Figure 6 is a curve illustrating the bandwidth obtained by the-antenna in Figure 4. Y

Figures '7 and 8 illustrate in side View and in section a further modification of the present invention. r

Referring now to Figures 1 and 2, reference numeral Ill denotes a plane conductive surface such as the wing surface or a substantially fiat part of the fuselage of an airplane. v

A pair of V-shaped or L-shaped slots l2 and M are cut in the conductive sheet llLthus forming a pair, of conductive triangles l8 and 20 separated by acentral slot 16. On the rear. surface of the conductive sheet I0 is fastened a flat 'metal pan 22 having such dimensions as to provide cavities 2|, 23 back of triangles I8 and 20 having an efiective depth of the order of one quarter of the operating wavelength. Thus, the triangles l8 and 20 are effectively isolated from the remainder of sheet 10. Back of the central slot l6 and in communication therewith is a feed chamber 24 entirely enclosed except at its point of connection with feed slot l6 and at its point of connection to transmission line TL. The dimensions of chamber 24 are so chosen that the chamber together with feed triangle 26 com"-' pletes the resonance at operating frequency. The inner conductor of transmission line TL is connected to the apex of the feed triangle 26, having its base connected to one edgeotfe'ed 'slot 15. High freouency energy arriving through transmission line TL passes through the feed chamber 24 ener izing the triangular radiating members l8 and 20 through slot l6.

Frorna consideration of Figure 3, wherein the cur fl v t h f ta d n er a i a 015 nates against frequency change in percentages j 'bscissae, it will'be noted'that overfa band extending about sixteen percent of the midband freq ency, the standing wave ratio falls reasonablvbelow 2:1.

The'antenna in Figures 1 and 2 has low mag nitude side lobes 'anfdi's smaller than" the ribbon t pet'rt'can be made sinaller'by capacity loadin at the free ends of the triangles. 'The band widths willho'wever, sufifer from such procedure. H wever the boundary slots may be omitted for services p rmitting the presence of side lobes in the radiation pattern of th antenna.

The present invention including this modification is shown in Figures 4 and 5. Herein the transmission line TL feeds into a rear cavity or chamber 34 having an equilateral triangular onne o fir i lar to thatde rh d with reference toFimire 2, Cayity or chamber 34 is ec a la n. orm ha inga de e t of t e order of .55 of the o eratin wavelength. It was foundthat radiating directly from a slot inthis cavity: tended; tosomewhatjrestrict the bandwidth of the; antenna: Therefore, an intermediate cavity 36 is provided between the conductiv'e sheet and the feed cavity 34. These cavities orchambers are coupled together by a single diagonal slot 35. Cavity 36 is coupled to "con d'uctiv'e" sheet ID by 'radiating"'slots 38 and 40, separated by'a distance of the order of .15 of the operating wavelength. The'depth of cavities 34 and 36 may be of the order of .07 of one wave length;

Back of the strip between th slots is prismatic conductive strip 42 triangular in cross section and con'ductively connected to the sheet IE3 at its ends. Studs 44 and 4!; connect strip 42 at two separated points to the back of rear cavity 34. These studs insure that only the desired mode' of'o's'cillation canbe set up within the-chambers. Aside from complete modestability' a} somewhat greater bandwidth isithusprovidedthrough the ability to choose proper coupling parameters between input and slots. It will be noted that due to the omission of: the outer insulating cavities a considerable reduction of the cutting up of sheet ID has been achieved Whileat'th" same tiinelthelf structure has been made mechanically more rugged; r

Figure 6 which is similar in nature to Figure 3 illustrates that for abandwidthinexcess of eighteen percent of .th'' midterm frequency, the antennashown in Figures i'andfi ha a'lo'w and fairly constant standing wave ratio. The operating band width is indicated in the figure.

It will further be noted from Figure 6 that the antenna of Figures 4 and 5 has high pass filter 5 characteristic. This is indicated by the way the curve of Figure 6 rises abruptly at the low frequency end of the characteristic but very slowly at the high frequency end. The usefulness ofrthe an tenna does not therefore end abruptly at the high frequency end. "Figures 7 and 8 illustrate a further modification 'offllihe invention which in effect constitutes afolding of the, chambers of the modification 'shownFigures 4 and 5 back to back against one atnothergThus arranged, the feed chamber extends back perpendicularly to the plane of conductive sheetilfl as a pair of triangular adjacent chambers 34 and 34'. Feed chamber 34 contains an equilaterally triangular transmission line coupler 26 similar to that in the modifications h wn nj hep usfi t -l The spa cirigj betweenthe' apex of feed triangle 2B and asidewall o f'chajinbef fl is maintained by an rinsulating spacer 5t. By varyingthe length of theinsulating'spacer and' thus the le betwe e ali e' fi its 3 11 W11? the s'pacin'g'"mayf be varied and thus input da ce. "may" r ed 159'- a P L r de? proper matchbetwe'en the antenna and a transmission line TL. Qn either sideof 'brs as: difllia t prbud hi r's" l r ia eq i b rs.5 1 3 1 51,? ,7 as and, are equivalentin' their operationt chambers 2 I and 3 of ur s 1 ndlandto t e sine eq ectangu 35 Iar'chambe'rBsjoiFigur clearly understoodthat it is not limited thereto s ncamany; m difi aiionsmar he. made. 11'1" ev ra ..e sm nts mp oyed nd inv e r a nssm gt' ithw d nartina om hes i a d. scope of the invention.

ha s cl ssed. s. I ies. antenna n lu i ea q duc re sheet. avin a Pair i. elqngei d a a l Slots th r 'u'i; a first rectangular chamber backof said sheet, said slots lying diagonally across said chamberlia second rectangula ilchainber backlof said first chamben' saidfsecond c'ha rnbei', M having a" single slot therein common to bothjjof said chambers, andmeans fo introducingihigh frequency ener y into said s ec nd chamber W) 2 An m ga man; hg a conductive sheet having a pair oj 'elonga d parallel slots therein; a first"recti' u1ar" et;

carca s a second rectangular chamber back of said firstchamber, said second chamber having a single slot therein common to both of said chambers, and means for introducing high frequency energy into said second chamber, said means including a triangular plate having its base connected along an edge of said single slot and its apex connected to a conductor of a transmission line.

3. An antenna including a conductive sheet having a pair of elongated parallel jslots therein," said slots having a length of substantially 0.65 wavelength at the operating frequency, a first rectangular chamber back of said sheet, said slots lying diagonally across said chamber, a second rectangular chamber back of said first chamber and having a single slot connecting both of said chambers, and means for introducing high fre-. quency energy into said second chamber, said means including a triangular plate having its.

base'connected along an edge of said singleslot and its apex connected to a conductor of a transmission line.

' 4. An antenna including a conductive sheet having a pair of elongated parallel slots therein,

said slots being spaced apart a distanceequal to 0.15 wavelength at the operating frequency, a

first rectangular chamber back of said sheet, said slots lying diagonally across said chamber, a second rectangular chamber back of said first chamber and having a single slot therein common 5. An antenna including a conductive sheet having a pair of elongated parallel slots therein, said slots having a length of substantially"0.65 wavelength at the operating frequency and said slots being spaced apart a distance equal to 0.15-

wavelength, a first rectangular chamber back of said sheet, said slots lying diagonally across said chamber, a second rectangular chamber back of said first chamber and having a single slot therein common to said chambers, and means for introducing high frequency energy into said second chamber, said means including a triangular plate having its base connected along an edge of said single slot and'its apex connected to a conductor of a transmission line.

'6.'An antenna including a conductive sheet having a pair of elongated parallel slots therein, a first rectangular chamber back of said sheet, said slots lying diagonally across said chamber, a second rectangular chamber back of said first chamber and having a single slot therein commonto both of said chambers, and means for. introducing high frequency energy into said seca first rectangular chamber back of said sheet,

said slots lying diagonally across said chamber, a second rectangular chamber back of said first chamber, a single slot common to said chambers,

and means for introducing high frequency energy into said second chamber, said rectangular chambers having a side length of 0.55 wave-- length at the operating frequency and an overall depth of substantially 0.07 wavelength at said frequency. 8,- An antenna including a conductive .sheet chamber. and having a single slot therein commonto said chambers, and means for introducing .'.high frequency energy into said second chamber, .there being a prismatic conductive strip between 'saidslots in said first chamber.

-' .9. An antenna including a conductive sheet having apair of elongated parallel slots therein,

. a first. rectangular chamber back of said sheet,

0.07-wavelength atsaid frequency, there being;

said slots lying. diagonally across said chamber,. a second rectangular chamber back of said first.

' chamberand having a single slot therein com-- mon to both of said chambers, and means'for' introducing high frequency energy into said secondchamber, said'rectangular chambers having. a side length of 0.55 wavelength at the operating frequency andan overall depth of substantially a prismatic conductive strip between. said slots; in said first chamber.

. 10. An antenna including a conductive sheet having a pair of elongated parallel slots therein.

a first rectangular chamber back of said sheet,

said slots lying diagonally across said chamber,

a second rectangular chamber back of said first chamber and having a single slot therein common to said first and second chambers, and

means for introducing high frequency energy in-.

to said second chamber, said means including a triangular plate having its base connected along an edge of said single slot and its apex connected to a conductor of a transmission line, said rectangular. chambers having a 'side length of 0.55 wavelength atthe operating frequency and an overall depth of substantially 0.07 wavelength at said frequency, there being a prismatic conductive strip between said slots in said first chamber.

11. An antenna including a conductive sheet having a pair of elongated parallel slots therein,

a'first rectangular chamber back of said sheet,.

said slots lying diagonally across said chamber,

a prismatic conductive strip having an apex and.

a base arranged between said slots in said first:

chamber and a pair of conductive studs from. the. apex of said strip to said rear wall of said second chamber.

12. An antenna including a conductive sheet. having a pair of elongated parallel slots therein, said slots having a length of substantially 0.65 wavelength at the operating frequency and said slots being spaced apart a distance equal to 0.15

wavelength at said frequency, a first rectangular chamber back of said sheet, said slots lying diagonally across said chamber, a second rectangular chamber having a rear wall and being arranged in back of said first chamber and having a further slot interconnecting said chambers, and means for introducing high frequency energy into said second chamber, said means including a triangular plate having its base connected along an edge of said further slot and its apex connected to a conductor of a transmission line; said rectangular chambers having a side length of 0.55 wavelength at said frequency and anoverall depth of substantially 0.07 wavelength agsvdsa 7 atsaidfirequency, v there being a prismatic conductivestriphaving an apex and a base arranged between saidslots in said-first'chamber-andj a pair of-conductive studs from the apex of said striptosaid rear wall for said" second chamber.

13; 'An antenna including a pair of' parallelij elongated slots in aplane conductive sheetga chamber arranged in back. of said" slots, said chamber including two jparallel triangular. wall" portions normal to; the'plane of said' sheet, said. 1 chamber; haying the base thereof surrounding said slots; partitions within said'chamber paral lelto said 'triangular ,wall portions and dividing sai d chamber into four. inner chambers sider by side; said inner chambers opening together into 15 asingle area at'the base of the first saidchamber and a triangular plate within one of the inner chambers, the base of said triangular plate being connected to an edge of'one of said partitions and a conductor of a transmission line being, 0 connected to the apex ofsaid triangular plate.

147' An antenna including a pair of para llel elongated slots in a plane conductive sheet,1a chamber arranged in back; of said slots, saidr chamber including two parallel triangular walls arranged normal to the plane of said sheet, said chamber having the base thereof surrounding said; slots, partitions within said chamber. dividingsaid chamber into four inner chambers e y. i e. aid hambe s, p c getherinto a single area at the base of ,thefirst said chamber and a triangular plate withinrone of theinner chambers, the base of said triangu,- lar plate being connected to an edge of oneof id. a titi n econduc q of a ansm ss o 9 Qnncs ted. Q; e-, pe2 of d trian ar. plate and means for adjusting the spacingnat the apex of said trianglefron the adjacentpar; tiaa 15.1An antenna including, a pair of parallel elongated slots inua planeconductivesheet, a chamber arranged. behind said slots, said chamber includingitwor parallel triangular wall' ,por-, ti ll sw arranged normal to. the plane, of said sheet, said ,slots lying betwe en said wall portions, partitions within said chamber dividing said chamberv into, four inneixchambers side by, side, saidinnfir chambers opening togetherinto asingle areaatothe base ofthefirst; said chamber, a triangulan plate withinone ,of the vinner; chain-w 5Q bers, the baseuof, said .triangular,, plate being, connected to; anedge pf one of said,.partitions,:a,, conductor of a transmission line connected to, apex, of said triangularnplate,andv aprismatic-J conductive member between said slots withinthe singlev area .in said. triangular chamben,

16 .An vantennamincluding.,a ,pair of parallel elongated-slots in a planeconductive sheet, ;a-- chamber arranged behind said slotsnsaidx chamberincluding two parallel triangular: wall .apor tions arrangednormal to theplane of said sheet,- said slots lyingbetween-said walliportions, parti-l-t tions ;within saidchamber dividingwsaidcharm ber: intolfour inner chambers side by side, said; inner echambers openingtogether into a sin lfi area-atthe base-0f ,theiirst said chamben a triangular plate within-oneof theninner cham bers, the base of said triangular platebeingcon nected. to anedge-of one'of ,said partitions-,a t prismatic conductive member between said slots, within the single area insaid triangularcham: ber; and connections from the apex of said ,Dr m aticmemberto the adjacentl edge of one ,of; p r ti ns-.1;

17. An antenna including a conductive sheet A V 8"; having'atleast one elongated=slot therein; a resonant chamber arranged behind said slot ,in saidsheet, atriangular plate within said chamber, saidxplate'having its base connected'to an edgeof said slot and a transmission line having a conduct'or connected to the apex of saidtrin l 18; "An antenna including a conductive sheet hayin at, least-one, elongated slot therein-,. a chamber arranged behindsaid slot in, said sheet,.

a trian ulait plate withinsaid, chamber, said. plate having, its base, connected to anedge of saidslot 'and. a .transmission line having a con,--

ductor connectednto ,theapexof said triangle,

said, chamber being, so dimensioned as to be resonant to theoperating frequency of said an-, tenna.

19. .An N antenna including a conductive sheet,

havingatleast one, elongated slot. therein, con,

ductive v,w a1l .,portions, forming a, chamber. back,

of said sheet having an aperture inone side.

thereof, there being alsubstantially unobstructed passagewaybetween said slot andrsa-id aperture,- atrian ular-plate within said chamber, said'plate havingathe -basegthereof connected to an edge;

of-rsaidaperture, and-means for connecting a conductor of a transmission -line tothe apex-of saidtriangular: plate.-

20.-An antenna including a conductive sheet having atleast oneelongated slottherein; con ductive wall portions forming a chamber back of said sheethavingan aperture in one side there of; there being; a substantially unobstructed pas-a sageway between 1 said-slot and said-aperture, av triangular plate within said "chamber; saidplate having the base thereof connected toan edge of;- said aperture; and -m-eans for connecting- I a: conductorof a-transm-ission' line to the-v apex' ofa said; trian marplate; said ,-chamber beingvdi mensioned to be -resonant-to the operating? fre quency of said antenna.- a

21; An antenna including a conductivesheet having; at least one elongated slottherein, a res+ onant chamber behind said slot in saidsheetrav triangular; plate; withinsaid chamber, said-plate havin'ga itsabasesconnected' to anedge of said slot and 'a transmission: line having -a' conduc=- tor'connected to ithesapex of said triangle, said:- sheet having 'V-shaped' slots disposed therein with the ends ofl saidslotsjuxtaposed to deer fine a quadrangular area in said sheet withisaid elongated slotdiagonally disposed in said area."

with the ends of said elongated slot adjacent the" ends of said V-shaped slots.

22; An; antennadncluding a conductive sheet having at least oneelongated slot therein, a-

chamber behind said slot in said sheet, a triangular plate withingsaid chamber, said plate with-theends of said slots juxtaposed to definea quadrangular area in said sheet with the/endsofsaidelongated slot adjacent the ends of said V-shaped slots," said chamber being dimensioned to beresonant to the operating, frequency of said antenna; V

23:'An antenna including a conductive sheet hflVi fiJl13 Sl7 one elongated slot therein, said: sheet having further-\L-shaped slots therein dis=y posed therein'with the ends of said slots J'ux-,

taposedto define a rectangular area in saidsheet with'said elongated slot diagonally disposed'in said area with the ends of said elongated slot adjacent the ends of said *V-shaped slots, and means for inducing high frequency energy in the area enclosed by the edges of said elongated slot, said means comprising a chamber arranged behind said elongated slot, a triangular plate within said chamber, said plate having the base thereof connected to an edge of said elongated slot, and means to connect a conductor of a transmission line to the apex of ,said triangular plate.

24. An antenna including a conductive sheet having at least one elongated slot therein, said sheet having further L-shaped slots therein disposed therein with the ends of said slots juxtaposed to define a rectangular area in said sheet with said elongated slot diagonally disposed in said area with the ends of said elongated slot adjacent the ends of said L-shaped slots, chambers arranged behind said L-shaped slots, each of said chambers having a wall constituted by a portion of said conductive sheet having one of said L-shaped slots therein, said chambers being so dimensioned as to present a high impedance to the operating frequency, and 6 means for inducing high frequency energy in the area enclosed by the edges of said elongated slot, said means comprising a further chamber arranged behind said elongated slot, a conductive triangle within said further chamber, said triangle having the base thereof connected to an edge of said elongated slot and means to couple a conductor of a transmission line to the apex of said triangle.

25. An antenna including a conductive sheet having at least one elongated slot therein, said sheet having further L-shaped slots disposed therein with the ends of said slots juxtaposed to define a rectangular area in said sheet with said elongated slot diagonally disposed in said area with the ends of said elongated slot adjacent the ends of said L-shaped slots, chambers arranged behind said L-shaped slots, each of said chambers having a wall constituted by a portion of said conductive sheet having one of said L-shaped'slots therein, said chambers having an effective depth of an odd multiple including unity of a quarter wavelength at the operating frequency, a further chamber arranged behind said elongated slot, a plane conductive member having an edge connected to an edge of said elongated slot and two other edges converging to a point, and means to connect a conductor of a transmission line to said member at said point.

NILS E. LINDENBLAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,206,923 Southworth July 9, 1940 2,226,479 Pupp Dec. 24, 1940 2,297,202 Dallenbach Sept. 29, 1942 

